The invention relates to measurement of surfactant concentration in an electrolytic solution and particularly to measurement of dilute organic additives in electroplating baths.
Surfactants are a class of materials which adsorb (stick) to the surface of a host material. It is often desirable to know the amount of a particular surfactant that is present in a liquid. For example, the concentration of surfactants is an important factor in electroplating. Electroplating involves the transfer of metal from an electrically conductive liquid (electrolyte) to a host metal.
In some cases, surfactants comprising various organic compounds are added to electroplating electrolytes to control the surface finish and mechanical properties of the resulting product. Since these additives may be consumed in the course of the electroplating process, it is desirable to monitor and adjust the additive concentration. In other cases, it is necessary to monitor the electrolyte to ensure that it contains no organic additives which under some conditions cause defects in the plating process.
U.S. Pat. No. 4,132,605 (Tench, et al.), discloses cyclic voltammetry and precisely controlled hydrodynamics to measure bulk metal deposition rates on a rotating disk working electrode. The deposition rate is correlated to additive concentration. The rotating working electrode, however, may be inconvenient in flow-through and handheld applications.
Each cycle in Tench requires more than one minute and generates a single data point; several data points are needed to reduce uncertainty in the measurement. There are many applications, however, in which greater speed and precision is desirable.
It is therefore an object of the invention to provide a fast and accurate measurement of surfactant concentration utilizing a stationery working electrode suited to hand-held wands and flow-through cells.